23 March 2010

The German Aerospace Center (DLR) is pursuing a program of space-mission development based on a standard satellite bus (SSB), suitable for missions and applications of different types. This project has the strategic objective of establishing within DLR the capabilities and facilities necessary for satellite development and operations.

Our proposed mission, AsteroidFinder, was selected as the first mission to use the SSB. The primary goal of the mission is to search for Inner-Earth Objects (IEOs), a particular class of Earth-approaching asteroids with orbits lying completely within the Earth’s orbit. Due to their proximity on the sky to the Sun, IEOs are extremely difficult to discover from the ground. By the end of September nearly 5700 Near Earth Objects (NEOs) have been discovered, of which only 9 are IEOs. Simulations have shown that AsteroidFinder may detect some dozens of IEOs in an operational period of two years and be able to characterize the population in terms of total number, orbit and size distribution.

A secondary goal of the mission is to demonstrate that the detection of cm-sized space debris is in principle feasible with a satellite-based optical instrument. To achieve its goals the mission has to detect small objects of various surface albedos, including extremely dark ones, near the direction of the Sun. This requires a limiting sensitivity of > 18.5 mag. Long exposure times (~ 1 min) and, therefore, a high pointing stability rate (~ 1 arcsec/s) are needed. Since this requirement is beyond the capability of the bus an order- of-magnitude improvement must be achieved at payload level. Stray light from the Sun, Earth and other objects must be effectively suppressed. The baseline payload of the AsteroidFinder mission consists of two main elements: the telescope and the electronic unit (EU). The EU contains the focal-plane array (detector), the corresponding front-end electronics, the digital-processing unit and power-supply unit. The data produced in the EU are stored in the mass memory of the satellite. The thermal control and telemetry are provided by the spacecraft bus. In 2008 a Phase-A study, in which several DLR institutes participated, successfully confirmed the feasibility of the project. Scientists in our Department were responsible for payload project management, for the scientific background of the mission, the definition of the scientific requirements, and for the observation strategy

Plans for the satellite -- which according to its builder, will be 80 centimeters wide and deep and 100 centimeters high, as big as a small refrigerator -- are slowly taking shape in Bremen. The plan is to have the satellite operational by 2013.

Work on the asteroid project is expected to last three more years. The pressure on the scientists behind the satellite will be huge if it flops. But nobody wants to think about that. Specifications for the satellite's individual components are expected to be completed by the end of the year, but there is still plenty of work to do. Afterwards, AstroidFinder will be built and then tested under the strenuous conditions it would undergo in outer space: It will be shaken, frozen and irradiated.

It is still unclear how AstroidFinder will be delivered to its orbit, between 650 and 850 kilometers above the Earth. DLR can either piggy back on another space mission or go the far more expensive route and purchase its own rocket. But that might be a small price to pay for a satellite that could help defend the planet from the deadly impact of an asteroid. Earth already bears scars -- in the form of craters -- all over its surface from previous asteroid assaults. And it would be prudent if we were able to predict the next impact before it happens.

"Asteroid Early Warning System: German Satellite to Help Detect Threats to Earth"
Christoph Seidler in Bremen
Der Spiegel
19 March 2010